FIGS. 1 and 2 of the accompanying drawings show a side view and a plan view of a well known aerator 1. The aerator 1 comprises four planar blades 2, 3, 4 and 5 which are secured to a cone-shaped boss 6. The diameter of such an aerator is typically 28 inches to 120 inches. In use, the boss 6 is secured to the drive shaft of a motor and the aerator is rotated in liquid, for example waste liquor at typically 25 to 120 r.p.m.
One of the disadvantages of this type of aerator is that under certain conditions the aerator produces excessive random quantities of extremely small droplets that could splash the aerator supporting bridge and adjacent structures. This is generally undesirable since the production of such extremely small droplets consumes a substantial amount of energy which is not rewarded with a commensurate increase in the air/liquid interface. In addition, excessive free board is required at increased installation costs.
Our observations have indicated that these excessive quantities of extremely small droplets are caused by droplets of water being thrown in the air by one blade, e.g. blade 2, and being hit by the next blade, e.g. blade 3, before they return to the liquid.
An object of at least preferred embodiments of the present invention is to provide an aerator which will produce less extremely small and random droplets than are produced by the aerator shown in FIGS. 1 and 2.
A further object of at least preferred embodiments of the present invention is to provide a mechanical aerator with low surging characteristics thereby enhancing the flow of liquid in the aeration vessel.
A still further object of at least preferred embodiments of the present invention is to provide a mechanical aerator which will not readily become covered in rags and similar items which are frequently found in waste water.
Another object of at least preferred embodiments of the present invention is to provide a mechanical aerator which, whilst being extremely simple and inexpensive to construct, has a high oxygenation efficiency.